Energy storage system with heat pipe thermal management

ABSTRACT

An energy storage system includes multiple cells, a heat pipe, a first heat transfer channel, and a second heat transfer channel. Each cell has a first end with anode and cathode terminals and a second end opposite the first end with the multiple cells arranged so that the second ends are aligned. The heat pipe has a U-shape and includes an evaporation portion having a flat evaporation surface facing the second ends of the multiple cells, a first condensation portion oriented substantially perpendicular to the evaporation portion, and a second condensation portion oriented substantially perpendicular to the evaporation portion. The first condensation portion is at a first end of the evaporation portion and the second condensation portion is at a second end of the evaporation portion. The first heat transfer channel abuts the first condensation portion and the second heat transfer channel abuts the second condensation portion.

CROSS REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120 as a continuation of U.S. Utility application Ser. No.14/189,219 entitled “ENERGY STORAGE SYSTEM WITH HEAT PIPE THERMALMANAGEMENT”, filed 25 Feb. 2014, which is hereby incorporated herein byreference in its entirety and made part of the present U.S. Utilitypatent application for all purposes.

BACKGROUND

Energy storage systems are used in a variety of contexts. For example,an electric vehicle can have a number of individual energy storage units(e.g., lithium-ion cells) stored inside a compartment, and this systemis often referred to as a battery pack. Cells and other storage unitsgenerate heat during operation, such as during the charging process andwhen the cells are used to deliver energy, for example to thepropulsion/traction system of the vehicle.

One cooling approach currently being used involves lithium-ion cellsthat are electrically connected by an anode terminal at the bottom ofthe cell, and a cathode terminal on top of the cell. These cells arearranged to all have the same orientation (e.g., “standing up”) withsome spacing provided between all adjacent cells. The spacingfacilitates a cooling conduit to run between the cells and be in contactwith at least a portion of the outer surface of each cell. The coolingconduit has a coolant flowing through it, which removes thermal energyfrom inside the battery pack to some location on the outside, where heatcan be safely dissipated. In order to provide a safe coolant flow, onemust provide fluid connections into and out of the battery package, andthe coolant path inside the battery pack must be reliable and haveenough capacity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of an assembly that is part of an energy storagesystem.

FIG. 2 shows an example of an energy storage system with heat pipes thathave an L-shape.

FIG. 3 shows another example of an energy storage system with heat pipesthat have an L-shape.

FIG. 4 shows an example of an energy storage system with heat pipes thathave a U-shape.

FIG. 5 shows another example of an energy storage system with heat pipesthat have a U-shape.

FIG. 6 shows another example of an energy storage system with one ormore heat pipes that have a U-shape, also including coolant tubes.

FIG. 7 shows an example of an energy storage system with linear heatpipes.

FIG. 8 shows another example of an energy storage system with the linearheat pipes from FIG. 7.

FIG. 9 shows an example of an energy storage system where heat pipeshave a deformation corresponding to a cross section profile of a heattransfer channel.

FIG. 10 shows another example of an energy storage system with heatpipes having a U-shape, with thermal tubes on top and bottom.

FIG. 11 shows another example of an energy storage system with heatpipes having a U-shape, with thermal tubes extending between manifoldspositioned at shorter sides of the system.

FIG. 11A is a cross section of the energy storage system in FIG. 11.

FIG. 12 shows another example of an energy storage system with heatpipes having a U-shape, with thermal tubes extending between manifoldspositioned at longer sides of the system.

FIG. 12A is a cross section of the energy storage system in FIG. 12.

DETAILED DESCRIPTION

This document describes examples of systems and techniques that provideface cooling of cells or other energy storage units by way of heatpipes. This can provide useful advantages, such as: The need forinternal fluid connections in a battery pack can be eliminated, therebyavoiding leakage; a closed loop cooling system can be provided thatreduces pressure drop losses with regard to an overall cooling system(e.g., in a vehicle); external cooling tube assemblies can beeliminated; rapid fluid migration can be provided that keeps cells ateven temperatures; cooling tube sections between rows of cells can beeliminated, thereby allowing more cells to be packed into a given space;and even if a rupture occurs in one of the heat pipe lumens, significantcooling/heating can nevertheless be provided by way of other undamagedlumens within the heat pipe.

FIG. 1 shows an example of an assembly 100 that is part of an energystorage system. Particularly, the energy storage system contains aninterconnected array of energy storage elements, two cells 102 of whichare shown here. In this example, the cells are physically secured andheld in place (e.g., to a particular torque value) by a pair of opposingclamshells: a top clamshell 104 and a bottom clamshell 106. For example,the clamshells have openings exposing the respective ends of each cell.In other implementations, the cells can be secured by a differenttechnique, such as by a structure interleaved between cells.

Here, a flexible printed circuit 108 overlies and connects electricalterminals of the cells 102. In this implementation, the flexible printedcircuit includes three layers: a flexible conductive layer 110sandwiched between a flexible bottom insulating layer 112 and a flexibletop insulating layer 114. The conducting layer can be a uniform layer ofmetal, such as copper, and the insulating layers can be uniform layersof polyimide (e.g., a Kapton® material). In other implementations, oneor more other materials can be used in lieu of or in combination withthe mentioned materials.

Here, the cells 102 are a type of rechargeable battery cell having aflat top with terminals at one end. Particularly, each cell has a centerpositive terminal 116 and a surrounding annular negative terminal 118.For example, the annular negative terminal can be part of, or mountedon, a main housing of the cell (e.g., the cell can) that extends alongthe length of the cell and forms the other end of the cell (i.e., thebottom end in this example).

The patterning of flexible printed circuit 108 produces die cut areas120 in the bottom insulating layer 112 to allow exposed portions ofconductive layer 110 to make electrical contact, for example toselectively connect to the terminals of the cell(s). Here, die cut areas122 in top insulating layer 114 allow exposed portions of conductivelayer 110 to receive a device that produces an electromechanicalconnection between the portion of conductive layer interacting with thedevice and the underlying surface to be joined (e.g., a terminal of oneof the cells 102). Any of several different types of devices andtechniques can be used in making the electromechanical joints. Forexample, spot welds 124 here join portions of the conductive layer 110to respective terminals of the individual cells.

The energy storage system can be implemented as a source of propulsionenergy in an electric vehicle, to name just one example. That is, anumber of cells can be interconnected in the energy storage system toform an array (e.g., a battery pack) that powers the vehicle. In otherimplementations, the illustrated assembly can also or instead poweranother aspect of a vehicle, or can be used in a non-vehicle context,such as in a stationary storage.

In the illustrated embodiment, the cells 102 are oriented vertically,and are shown standing on a heat pipe 126. The heat pipe can beconnected to a thermal management system (not shown) to provide forthermal management of the energy storage system. Cooling of the cells102 can be performed using an evaporation end 126A that faces the cells,and at least one condensation end 126B. The evaporation end can extendfor at least the entire length required by the array of cells, or partthereof. Here, the heat pipe 126 has an L-shape when viewed from theside, with the condensation end elevated above the evaporation end. Inother implementations, the heat pipe can have a different shape. Forexample, and without limitation, more than one condensation end can beprovided. In some implementations, the heat pipe can instead provideheating of the cells and the rest of the energy storage system.

In this example, the assembly 100 has an electric insulator layer 128between the evaporation end 126A of the heat pipe 126 and the bottom ofthe cells 102. This layer prevents electric contact between the heatpipe (which can be a metal component) and the cell housing. For example,a thermal interface material (TIM) can be used to electrically insulatean anode terminal at the bottom of the cell while allowingcooling/heating of the cells through the same surface. In someimplementations, the assembly is manufactured by applying the electricinsulator layer on the heat pipe, applying adhesive onto the top of thelayer (e.g., at each cell position), and then positioning the cell orcells on the layer.

The heat pipe can be manufactured from any suitable material. In someimplementations, the heat pipe can be extruded from metal and have atleast one interior channel for the phase-change fluid. The interiorchannel(s) can have one or more features that aid the flow of fluid inthe liquid phase and/or gas phase. For example, a groove, powder and/orsponge can be provided inside the heat pipe.

FIG. 2 shows an example of an energy storage system 200 with heat pipes202 that have an L-shape. In this example, an evaporation surface 202Ais oriented essentially horizontally (e.g., inside a battery pack of anelectric vehicle) and a condensation surface 202B is orientedessentially vertically. A module 204 of cells (e.g., lithium-ion cellsof the 18650 type) is here shown positioned on one of the heat pipes.The interface between the module and the heat pipe is by conductivethermal contact requiring a TIM. For example, the heat pipe can comprisemultiple adjacent parallel heat sections attached to each other (e.g.,by welding). The module can have more or fewer cells than illustrated inthis example, and/or the cells can be arranged in a differentconfiguration. For clarity, only one module of cells is shown here.Implementations of energy storage systems can have any number ofmodules.

The energy storage system 200 has at least one heat transfer channel 206that is in thermal exchange with the heat pipes 202. In someimplementations, an auxiliary system can circulate fluid, such ascoolant, in one or more channels inside the heat transfer channel. Forexample, the energy storage system described here can be incorporated asa battery pack in an electric (or hybrid) vehicle, and a cooling systemexternal to the battery pack can then cool the fluid from the heattransfer channel, thereby removing heat from the cells.

Here, the heat transfer channel 206 is provided in the middle of theenergy storage system 200, and the module 204 and other modules can thenbe positioned in rows on each side of the channel, for example in alocation 208. The condensation ends/surfaces of the respective heatpipes are here positioned so that they about the sides of the heattransfer channel. Accordingly, the heat pipes extend from the channel inopposite directions. Here, the heat pipe 202 on which the module 204 ispositioned is shown to consist of six parallel heat pipe sections.Solely as an example, each of such sections can contain 14 separateinternal channels, each of which individually operates according to theprinciple of a heat pipe.

FIG. 3 shows another example of an energy storage system 300 with heatpipes 302 that have an L-shape. Each of the heat pipes has a module 304of cells associated with it. The cells are aligned with each other sothat one of their ends (e.g., the bottom end, or a negative end) facesan evaporation surface 302A of the heat pipe. In this implementation,the cells are positioned essentially horizontally and the evaporationsurface is vertical. A condensation surface 302B of the heat pipe,however, is elevated above the evaporation surface and is horizontal inthis example. In some implementations, a cooling surface can be formedby all the condensation surfaces collectively, or can be a separatesurface applied on top of them. Such a cooling surface can then be usedfor removing heat from all of the cell modules. For example, the coolingsurface can be provided with a common active cooling channel (analogousto the heat transfer channel 206 of FIG. 2); heat spreaders transverseto the cooling channel can then accumulate heat from the respectivecondensation surfaces and transport that heat to the cooling channel.

FIG. 4 shows an example of an energy storage system 400 with heat pipes402 that have a U-shape. That is, each of the heat pipes has anevaporation surface 402A and two condensation surfaces 402B, one ateither end of the evaporation surface. Each of the heat pipes has amodule 404 of cells associated with it. For example, this system can beuseful in a vehicle, because the U-shaped heat pipes provide increasedindependence from angularity changes (e.g., when the vehicle isoperating on an inclined and/or graded surface).

The energy storage system has a central heat transfer channel 406 andone or more side heat transfer channels 408, each of which is in thermalexchange with the heat pipes 402. Here, the side heat transfer channelsare provided at the ends of the heat pipes opposite the central heattransfer channel. In this implementation, the heat pipes are orientedalong the length of the modules 404. For example, this energy storagesystem can provide an advantageously small ratio of condensation arearelative to evaporation area, which allows the cooling tube to occupy arelatively small volume of the battery pack.

FIG. 5 shows another example of an energy storage system 500 with heatpipes 502 that have a U-shape. Each of the heat pipes has an evaporationsurface 502A and two condensation surfaces 502B, one at either end ofthe evaporation surface. Each of the heat pipes has a module 504 ofcells associated with it. The energy storage system has a central heattransfer channel 506 and one or more cross member heat transfer channels508, each of which is in thermal exchange with the heat pipes 502. Thecross member heat transfer channels are transverse to the centralchannel; for example, the cross member can extend equally far on bothsides thereof. A heat transfer medium (e.g., coolant) can flow in theheat transfer channels to provide thermal exchange with the heat pipes.Here, the heat pipes are oriented across the width of each batterymodule. For example, this energy storage system can provide anadvantageously small ratio of condensation area relative to evaporationarea.

FIG. 6 shows another example of an energy storage system 600 with one ormore heat pipes 602 that have a U-shape, also including coolant tubes604. Each of the heat pipes has an evaporation surface 602A and twocondensation surfaces 602B, one at either end of the evaporationsurface. This example shows a module 606 of cells in the energy storagesystem. For example, during operation the heat pipe can convey heat inboth directions along the evaporation surface, towards each respectivecondensation surface. That is, the thermal flow inside the heat pipe ishere parallel to the plane of this drawing.

This energy storage system also has the coolant tubes 604 that are inthermal exchange with the heat pipes 602. In this example, each of thecoolant tubes has an essentially L-shaped profile. For example, theprofile of the L-shape can at least partially correspond to the outersurface of the U-shaped heat pipe. This provides an advantageously largesurface area of contact between the coolant tube and the heat pipe,which facilitates thermal exchange between them. The coolant tubes 604can provide reversibility (i.e., the ability to do both heating andcooling) of the heat pipe. For example, the L-shaped profile of thecoolant tubes facilitates removal of heat from the evaporation surface602A during cooling of the module, and also delivery of heat from thecondensation surfaces 602B to the module during heating. As anotherexample, the shape and configuration of the system in this example canhelp reduce gravitational issues that might otherwise occur, such as ifthe grooves of the heat pipe are not manufactured to give effectivecapillary force. This configuration can also improve the way that theU-shaped heat pipe is packaged inside a housing or other structure thatholds the energy storage system.

The coolant tube has one or more interior channels in which coolant canbe circulated within the system (i.e., the coolant can flow indirections into, and out of, the plane of the figure). The two coolanttubes in this example can have coolant flowing in the opposite, or thesame, direction as each other. In some implementations, the coolant tubecan be used for providing reversible thermal transfer, such that theenergy storage system can be cooled or heated depending on what isneeded. For example, the condenser contact here extends onto the flatportion of the heat pipe and can therefore also be used for deliveringheat (e.g., from an external heating system) into the heat pipe, fromwhere the heat then flows into the individual cells.

FIG. 7 shows an example of an energy storage system 700 with linear heatpipes 702. Each of the heat pipes has a module 704 of cells associatedwith it. The energy storage system has a central heat transfer channel706 that can have coolant flowing through it. Here, an end portion 702Aof each heat pipe serves as an evaporation area, and a central portion702B of the heat pipe (i.e., near the heat transfer channel) serves as acondensation area. The internal channel(s) of the heat pipe can betruncated at the central heat transfer channel, or can extend along thelength of the heat pipe. This energy storage system can provide arelatively large ratio of evaporation area relative to condensationarea, and can work reversibly (i.e., to provide heating instead ofcooling). Also, this implementation can be efficient in terms ofvolumetric energy density.

FIG. 8 shows another example of an energy storage system 800 with thelinear heat pipes 702 from FIG. 7. The system here also has the module704 of cells, and the central heat transfer channel 706. In addition,the system has one or more side heat transfer channels 802 through whichcoolant can flow. For example, the side channel(s) can be positioned atthe ends of the heat pipes. This system can be useful in a vehicle,because the positions of the central and side heat transfer channelsprovide increased independence from angularity changes (e.g., whenoperating the vehicle on an inclined and/or graded surface). As anotherexample, the system can provide reversible heat transfer, such as forheating the cells instead of cooling them.

FIG. 9 shows an example of an energy storage system 900 where heat pipes902 have a deformation 904 corresponding to a cross section profile of aheat transfer channel 906. That is, while the heat pipes are heregenerally linear in areas where the battery cell modules are located,the heat pipe here has the deformation so as to conform a condensationend of the heat pipe to the shape of the heat transfer channel. Theinternal channel(s) of the heat pipe can be truncated at the centralheat transfer channel, or can extend along the length of the heat pipe.For example, this system can provide a smaller ratio of condensationarea relative to evaporation area than a corresponding L-shape heatpipe.

FIG. 10 shows another example of an energy storage system 1000 with heatpipes 1002 having a U-shape, with thermal tubes on top and bottom. Eachheat pipe encloses a module 1004 of cells, only one of which modules isshown here for simplicity. The heat pipes are organized so that thesystem has four heat pipes across its width, and three (sets of four)heat pipes along its length. Other configurations and/or numbers of heatpipes can be used in other implementations. For example, and withoutlimitation, the energy storage system could have a width of one heatpipe. In yet another implementation, one or more heat pipes can insteadbe transverse to the length of the energy storage system.

Here, the energy storage system 1000 is arranged so that the largersurface of the heat pipes—i.e., the one abutting the non-terminal endsof the cells—is generally vertical. The two opposing heat pipesurfaces—which abut the side surfaces of the outermost rows of cells—aregenerally horizontal.

Thermal tubes 1006 and 1008 are placed on the top and bottom of the heatpipes, respectively. Each thermal tube is manufactured of a materialwith sufficient thermal conductivity to absorb heat from, or deliverheat into, the heat pipes through the facing surface. For example, thethermal tube can have a number of internal channels configured forhaving a fluid (e.g., coolant) flowing therein. As such, the thermaltubes can be connected to an external cooling/heating system (notshown), which can be located outside the housing of the energy storagesystem.

As a first example, both the thermal tubes 1006 and 1008 can be used forcooling the cells of the energy storage system by way of a flowingcoolant. In some implementations, coolant flows in opposite directionsin the two respective thermal tubes.

As a second example, the thermal tube 1006 (i.e., on top) can be usedfor cooling the cells, and the thermal tube 1008 (i.e., on the bottom)can be used for heating the cells. This configuration is advantageous inthat the heat pipe operates aided by gravity, rather than againstgravity, and is more efficient as a result. In a normally vertical heatpipe section the vapor will always move upward unless the vehicleorientation is rotated by at least 90 degrees. The above advantage cantherefore be relatively unaffected by vehicle orientation. Both when thebatteries are being cooled and when they are being heated, the lessdense vapor will move upward (opposite to gravity) and the fluid willmove downward (with gravity). That is, during operation, when the cells(and/or other electrical devices in the system) are generating heat, theupper thermal tube can serve to cool the system by way of removingthermal energy from the heat pipes. In contrast, when the cells (and/orthe rest of the energy storage system) need to be warmed up, such asbefore operating the system in a cold environment, the lower thermaltube can serve to warm the system by way of introducing thermal energyinto the heat pipes. For example, the flow of cooling/heating fluid canbe directed to either the upper or lower thermal tube, as applicable, byway of a valve, such as a solenoid valve.

FIG. 11 shows another example of an energy storage system 1100 with heatpipes 1102 having a U-shape, with thermal tubes 1104 extending betweenmanifolds 1106 and 1108 positioned at shorter sides of the system. Theheat pipes hold modules of cells adjacent the thermal tubes, of whichonly modules 1110 and 1112 of cells are shown for clarity. That is, inthis example the thermal tubes are parallel to the length of the energystorage system (e.g., a battery pack).

The manifolds 1106-08 and the thermal tubes 1104 have one or morechannels inside them to facilitate flow of a fluid (e.g., coolant) tovarious parts of the system. For example, the manifold 1108 can be theinlet manifold, receiving fluid from at least one inlet 1114, and themanifold 1106 can be the outlet manifold, with fluid exiting through atleast one outlet 1116. Between the two manifolds, the fluid passes inthe interior channels of the thermal tubes 1104, and in so doingprovides thermal exchange (e.g., cooling) of the cells by way of theheat pipes.

FIG. 11A is a cross section of the energy storage system in FIG. 11.Particularly, modules 1110 and 1112 of cells are shown positioned inheat pipes 1102A and 1102B, respectively. The heat pipes, in turn, arepositioned between respective thermal tubes 1104A, B and C. For example,in operation the heat from the module 1110 is conveyed by way of theheat pipe 1102A into the thermal tubes 1104A and B, whereas the heatfrom the module 1112 is conveyed by way of the heat pipe 1102B into thethermal tubes 1104B and C. Some configurations can have the heat pipesand/or thermal tubes arranged in other ways.

FIG. 12 shows another example of an energy storage system 1200 with heatpipes 1202 having a U-shape, with thermal tubes 1204 extending betweenmanifolds 1206 and 1208 positioned at longer sides of the system. Theheat pipes hold modules of cells adjacent the thermal tubes, of whichonly modules 1210 and 1212 of cells are shown for clarity. That is, inthis example the thermal tubes are transverse to the length of theenergy storage system (e.g., a battery pack).

The manifolds 1206-08 and the thermal tubes 1204 have one or morechannels inside them to facilitate flow of a fluid (e.g., coolant) tovarious parts of the system. For example, the manifold 1208 can be theinlet manifold, receiving fluid from at least one inlet 1214, and themanifold 1206 can be the outlet manifold, with fluid exiting through atleast one outlet 1216. Between the two manifolds, the fluid passes inthe interior channels of the thermal tubes 1204, and in so doingprovides thermal exchange (e.g., cooling) of the cells by way of theheat pipes.

FIG. 12A is a cross section of the energy storage system in FIG. 12.Particularly, modules 1210 and 1212 of cells are shown positioned inheat pipes 1202A and 1202B, respectively. The heat pipes, in turn, arepositioned between respective thermal tubes 1204A, B and C. For example,in operation the heat from the module 1210 is conveyed by way of theheat pipe 1202A into the thermal tubes 1204A and B, whereas the heatfrom the module 1212 is conveyed by way of the heat pipe 1202B into thethermal tubes 1204B and C. Some configurations can have the heat pipesand/or thermal tubes arranged in other ways.

As used herein, the term “heat pipe” is used in a broad sense to includea number of techniques, such as phase change thermal systems that usehighly conductive materials and have a substantially flat form factor.The term heat pipe includes, but is not limited to, grooved style heatpipes, heat pins, vapor chambers, pyrolytic graphite sheets, and othertechnologies where heat is transferred between interfaces by way ofthermal conduction and phase transition.

A number of implementations have been described as examples.Nevertheless, other implementations are covered by the following claims.

What is claimed is:
 1. An energy storage system comprising: multiplecells, each cell having a first end with anode and cathode terminals,and a second end opposite the first end, the multiple cells arranged sothat the second ends are aligned; a heat pipe having a U-shape, the heatpipe including an evaporation portion having a flat evaporation surfacethermally coupled to the second ends of the multiple cells, a firstcondensation portion oriented substantially perpendicular to theevaporation portion, and a second condensation portion orientedsubstantially perpendicular to the evaporation portion, the firstcondensation portion at a first end of the evaporation portion, and thesecond condensation portion at a second end of the evaporation portion;a first heat transfer channel abutting the first condensation portion,the first heat transfer channel configured to reject thermal energyfrom, or bring thermal energy to, the first condensation portion; and asecond heat transfer channel abutting the second condensation portion,the second heat transfer channel configured to reject thermal energyfrom, or bring thermal energy to, the second condensation portion. 2.The energy storage system of claim 1, further comprising electricalconnections interconnecting the multiple cells.
 3. The energy storagesystem of claim 1, further comprising at least one clamshell that holdsthe multiple cells in place.
 4. The energy storage system of claim 1,further comprising an electric insulator layer disposed between the flatevaporation surface and the multiple cells, the electrical insulatorbeing thermally conductive.
 5. The energy storage system of claim 1,further comprising a phase-change fluid within the heat pipe.
 6. Theenergy storage system of claim 5, further comprising at least oneinterior channel within the heat pipe that aids flow of the phase-changefluid.
 7. The energy storage system of claim 1, further comprising: afirst manifold coupled to first ends of the first and second heattransfer channels; and a second manifold coupled to second ends of thefirst and second heat transfer channels to enable flow of coolant fromthe first manifold to the second manifold through the first and secondheat transfer channels.
 8. The energy storage system of claim 1, whereinthe multiple cells are positioned so that the second ends are alignedwith a vertical plane and the flat evaporation surface extends along thevertical plane.
 9. The energy storage system of claim 1, wherein themultiple cells have cylinder shapes that are vertically oriented withrespect to the flat evaporation surface.
 10. An energy storage systemcomprising: multiple cells, each cylindrically shaped cell having afirst end with anode and cathode terminals, and a second end oppositethe first end, the multiple cells arranged so that the second ends arealigned; a flexible printed circuit that overlies and interconnectselectrical terminals of the multiple cells; a heat pipe having aU-shape, the heat pipe including an evaporation portion having a flatevaporation surface thermally coupled to the second ends of the multiplecells, a first condensation portion oriented substantially perpendicularto the evaporation portion, and a second condensation portion orientedsubstantially perpendicular to the evaporation portion, the firstcondensation portion at a first end of the evaporation portion, and thesecond condensation portion at a second end of the evaporation portion,wherein the multiple cells are vertically oriented with respect to theflat evaporation surface; an electric insulator layer disposed betweenthe flat evaporation surface and the multiple cells, the electricalinsulator being thermally conductive; a first heat transfer channelabutting the first condensation portion, the first heat transfer channelconfigured to reject thermal energy from, or bring thermal energy to,the first condensation portion; and a second heat transfer channelabutting the second condensation portion, the second heat transferchannel configured to reject thermal energy from, or bring thermalenergy to, the second condensation portion.
 11. The energy storagesystem of claim 10, further comprising a phase-change fluid within theheat pipe.
 12. The energy storage system of claim 11, further comprisingat least one interior channel within the heat pipe that aids flow of thephase-change fluid.
 13. The energy storage system of claim 10, furthercomprising: a first manifold coupled to first ends of the first andsecond heat transfer channels; and a second manifold coupled to secondends of the first and second heat transfer channels to enable flow ofcoolant from the first manifold to the second manifold through the firstand second heat transfer channels.
 14. The energy storage system ofclaim 10, wherein the multiple cells have cylinder shapes and arevertically oriented with respect to the flat evaporation surface.
 15. Anenergy storage system for containing multiple cells, each cylindricalshaped cell having a first end with anode and cathode terminals, and asecond end opposite the first end, the multiple cells arranged so thatthe second ends are aligned, the energy storage system comprising: aheat pipe having a U-shape, the heat pipe including an evaporationportion having a flat evaporation surface thermally coupled to thesecond ends of the multiple cells, a first condensation portion orientedsubstantially perpendicular to the evaporation portion, and a secondcondensation portion oriented substantially perpendicular to theevaporation portion, the first condensation portion at a first end ofthe evaporation portion, and the second condensation portion at a secondend of the evaporation portion; a first heat transfer channel abuttingthe first condensation portion, the first heat transfer channelconfigured to reject thermal energy from, or bring thermal energy to,the first condensation portion; and a second heat transfer channelabutting the second condensation portion, the second heat transferchannel configured to reject thermal energy from, or bring thermalenergy to, the second condensation portion.
 16. The energy storagesystem of claim 15, further comprising electrical connectionsinterconnecting the multiple cells.
 17. The energy storage system ofclaim 15, further comprising an electric insulator layer disposedbetween the flat evaporation surface and the multiple cells, theelectrical insulator being thermally conductive.
 18. The energy storagesystem of claim 15, further comprising a phase-change fluid within theheat pipe.
 19. The energy storage system of claim 15, furthercomprising: a first manifold coupled to first ends of the first andsecond heat transfer channels; and a second manifold coupled to secondends of the first and second heat transfer channels to enable flow ofcoolant from the first manifold to the second manifold through the firstand second heat transfer channels.
 20. The energy storage system ofclaim 15, wherein the multiple cells are positioned so that the secondends are aligned with a vertical plane and the flat evaporation surfaceextends along the vertical plane.